Integrated circuits, communication units and methods of cancellation of intermodulation distortion

Abstract

A wireless communication unit includes a transmitter for processing a baseband transmit signal to produce a first radio frequency signal. A receiver is arranged to convert a second radio frequency signal to a baseband receive signal, where the receiver has a summation module arranged to add a cancellation signal to the baseband receive signal. A selectivity element is arranged to couple the transmitter and the receiver to an antenna, where a reduced portion of the first radio frequency signal is introduced into the second radio frequency signal thereby creating a second order inter-modulation distortion component in the baseband receive signal. An adaptive estimator module has a filter for filtering the baseband receive signal to remove dc offsets associated with the second order inter-modulation distortion component and generate the cancellation signal based on the baseband transmit signal and the filtered baseband receive signal for inputting to the summation module.

Description

FIELD OF THE INVENTION[0001]The field of this invention relates to integrated circuits, communication units and methods of cancellation of intermodulation distortion. The invention is applicable to, but not limited to, second order intermodulation product distortion cancellation in integrated circuits and wireless communication units.BACKGROUND OF THE INVENTION[0002]For many years frequency division duplex (FDD) and time division duplex (TDD) have been the two methods of choice for handling uplink (UL) and downlink (DL) transmissions in wireless systems. FDD uses two different frequencies for the UL and DL thereby separating them in frequency whereas TDD utilises a single frequency for both UL and DL signals and separates them in time. Therefore, in order to meet the performance requirements of a number of telecommunications standards, integrated circuits (ICs) and / or communication units have been designed to utilise frequency division duplex (FDD) techniques as a mechanism to separ...

AI Technical Summary

Benefits of technology

[0014]In this manner, the actual transmit baseband, digital signal is used as a reference from which a digital estimate of the actual second order inter-modulation distortion component (IMD2) is generated. The adaptive estimator module comprises a filter arranged to filter the baseband receive signal to remove dc offsets associated with the second order inter-modulation distortion component. Thus, the adaptive estimator module generates the cancellation signal based on the baseband transmit signal and the filtered baseband receive signal for inputting to the summation module. In this manner, the digital estimate of the IMD2 is subtracted from the received digital signal in the summation module in order to provide a corrected version for the remainder of the receiver chain. An adaptive approach is employed to minimise the effects of mismodelling and to track out variations in the transmit-receive, IMD2 path dynamics, for example due to process, voltage, load and / or temperature variations.

[0020]According to an optional feature of the invention, the wireless communication unit may comprise a power measurement module operably coupled to the adaptive estimator module and arranged to measure an on-channel power level of the baseband receive signal. The adaptive estimator module comprises a baseband processing module arranged to determine an adaptation rate to be used by the adaptive estimator module in generating the cancellation signal based on the measured on-channel power level of the baseband receive signal. In this manner, a mechanism is described that provides an automatic regulation of adaptation rate to reduce second order intermodulation distortion.

[0028]According to a third aspect of the invention, there is provided a method for reducing a second order inter-modulation distortion component in a wireless communication unit. The method comprises processing a baseband transmit signal to produce a first radio frequency signal capable of wireless transmission; and receiving a second radio frequency signal comprising a portion of the first radio frequency signal that creates a second order inter-modulation distortion component in the baseband receive signal. The method further comprises converting the second radio frequency signal to a baseband receive signal; adding a cancellation signal to the baseband receive signal; filtering the baseband receive signal to remove dc offsets associated with the second order inter-modulation distortion component; and generating the cancellation signal based on the baseband transmit signal and the filtered baseband receive signal.

Problems solved by technology

As a consequence, and particularly at typical wireless communication frequencies where the transmit (and therefore receive) frequency is very high, such as in the 1 GHz frequency region in the third generation (3G) wideband code division multiple access (WCDMA) standard, it is known that interference is caused by poor isolation between the transmitted and received signals at these very high frequencies within the ICs or communication units.

Here, the transmit signal leaks through the duplex filter and mixes via the mechanism of second order distortion within the receive mixer to baseband, thereby resulting in degraded receive signal to noise ratio (SNR) performance.

This causes an effective desensitization of the receiver.

In this scenario, such 2nd order intermodulation products can ‘desense’ the radio and lead to bit-error-rate (BER) failure.

However, given the limitations of filtering technology at such high radio frequencies, a significant amount of the transmit signal is leaked 140 into the receiver path.

However, the use of SAW filters is no longer acceptable due to their large size and high cost factors, coupled to the ever-increasing need to minimise product cost and size, particularly in the mobile telephone handset business.

However, this solution suffers from the need to use multiple lumped element inductors.

However, it is believed that this approach may not be effective, as analogue radio frequency designs do not cope well across PVT.

Furthermore, there is a concern that the addition of a dedicated trimming port could potentially compromise other key RF metrics.

There are some disadvantages that exist in the related art, such as the selectivity of the receiver performance (when a bandwidth (BW) is, say, <100 Hz) comes at a disadvantage of too slow a settling time, for example due to any averaging technique used.

A further disadvantage that exists in the related art is that a fixed (and therefore rigid) value of adaptation rate is selected to work across the power range of the communication unit.

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